This application is based on PCT/EP02/03876, filed 8 Apr. 2002, which claims priority of German application No. 10119339.4, filed 20 Apr. 2001
This invention relates to a fuel cell system with a polyelectrolyte membrane fuel cell and a method by which the pressure inside the fuel cell can be regulated by means of the quantity of fuel introduced. This regulation is accomplished by means of pressure sensors which are controlled by means of an electronic control unit.
Miniaturized polymer electrolyte membrane fuel cells (PEMFC) are operated at a small overpressure of typically 50-100 mbar. Only a small overpressure is used in these fuel cell systems because, as a result of the miniaturization, the mechanical strength of the components is low compared to larger systems. Safety considerations also argue in favor of operation at small overpressures.
In fuel cells of the prior art, the fuel is first extracted from an accumulator in which a high overpressure is maintained. When hydrogen is used, for example, metal hydride in an accumulator at an overpressure of approximately 2-10 bar is used. For the delivery of the fuel from this accumulator into the fuel cell, it is therefore necessary to reduce the pressure. In similar systems of the prior art, this pressure reduction is accomplished by means of voluminous and heavy pressure reducers. The operating principle of this pressure reducer is based on an internal membrane which mechanically opens and closes the inlet valve, depending on the pressure differential, so that a defined constant overpressure is maintained downstream of the pressure reducer (Dubbel-Taschenbuch für den Maschinenbau, Section G 157, 16th Edition). However, this method requires membranes that have a large surface area, which runs counter to the demands of the miniaturization of the fuel cell. Therefore this method cannot be used to realize compact fuel cell systems.